• Solid Opal Solid Opals are one piece of solid Opal. Solid Opals are more valuable and expensive than doublet and triplet, as the whole stone is made up from opal. • Doublet Opal Doublet Opals are Opals which are made using a layer of precious Opal with either potch Opal, ironstone or plastic attached to the back. These opals are cheaper as some of the weight is not made up from opal. • Triplet Triplet Opal consists of three layers, a thin layer of precious Opal, a thicker quartz layer on top of the Opal, and plastic back. As triplet Opals consist of the least carat weight of Opal they are the least expensive opal.